Windows down vs. AC

[Timelessblur]

45 mphish. Myth Busters on discovery channel did exactly what your asking in as a controlled an experiment as they could. Windows up vs down. I’ll look for a link.

It is going to be a lot lower on a modern EV. Our EV are more heavily affect by aero drag increase and AC are more efficiency than the ones they tested.

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[Larry Paul]

It’s negligible.

If you don’t mind being miserable, you’ll save more energy opening the windows in your house and turning the HVAC off.

But your house is not driving. The issue the Mach E has has I think a signficant aerodynamic drag with open windows.

 

[Mach1E]

But your house is not driving. The issue the Mach E has has I think a signficant aerodynamic drag with open windows.

Which is why it’s negligible (the difference between open windows and AC).

Some people drive their houses:

 

[Reign of Ravens]

Another question that nobody is discussing is what temperature you're setting your AC to. Obviously higher settings will result in less energy being taken up. I usually have my A/C set to 74˚F; here in Hawaii the temperature is usually 80-86˚F during the times I'm driving. 74 gets me feeling cool to cold, fan speed and such set to auto, and it really doesn't consume much energy.

If we want to be complete, we could also ask the question of how much tinting the windows would save you on A/C usage, too. I have the glass roof and Ford's tinting makes it so I don't feel any heat coming through the roof. Rear windows aren't tinted as heavily but are similar. When I get rays of sun hitting me through the front windows it's jarring by comparison, because it feels very warm. I'd guess there's some data on this... just another efficiency consideration.

 

[babgvant]

45 mphish. Myth Busters on discovery channel did exactly what your asking in as a controlled an experiment as they could. Windows up vs down. I’ll look for a link.

This could (probably will) vary from car to car, and wind direction. It's highly unlikely that there's a one-size-fits-all number.

In a car that was designed with minimizing drag as a primary design goal, I would expect it to be a lower speed.

On a bicycle, the magic number where aerodynamics starts to matter is ~12 mph. That's when changes in body position, what you wear, how deep your wheels are, etc. start to mean something tangible. You want the air to attach at the front of the object and stay attached for as long as possible, having the windows open would likely cause detachment, which is a bad thing.

It should be possible to measure this fairly accurate by using a OBD II and a data logger as long as the Mach-E provides real-time (ish) consumption.

 

[Mach1E]

This could (probably will) vary from car to car, and wind direction. It's highly unlikely that there's a one-size-fits-all number.

In a car that was designed with minimizing drag as a primary design goal, I would expect it to be a lower speed.

On a bicycle, the magic number where aerodynamics starts to matter is ~12 mph. That's when changes in body position, what you wear, how deep your wheels are, etc. start to mean something tangible. You want the air to attach at the front of the object and stay attached for as long as possible, having the windows open would likely cause detachment, which is a bad thing.

It should be possible to measure this fairly accurate by using a OBD II and a data logger as long as the Mach-E provides real-time (ish) consumption.

On a bicycle where you have less
Than 1 horsepower and horrible aerodynamics, yeah, it matters more.

1/2 horsepower of drag on a bicycle means you’re going nowhere.

1/2 hp of drag on a car? You’ll never notice.

 

[babgvant]

On a bicycle where you have less
Than 1 horsepower and horrible aerodynamics, yeah, it matters more.

1/2 horsepower of drag on a bicycle means you’re going nowhere.

1/2 hp of drag on a car? You’ll never notice.

My CdA on my TT bike is lower than the Mach-Es ...

The larger point is that physics applies universally. 1/2hp is 1/2 hp, you might not notice it, but it's still there and should still be measurable.

 

[SnBGC]

More efficient with windows up and A/C on.
Remember, the A/C compressor is running anyway so might as well get the benefit.

 

[Mach1E]

My CdA on my TT bike is lower than the Mach-Es ...

The larger point is that physics applies universally. 1/2hp is 1/2 hp, you might not notice it, but it's still there and should still be measurable.

Yes it’s measurable.

So is the 1/2 hp that an a/c system uses.

So if you’re comparing 1/2 hp from a/c vs 1/2 hp from windows down drag…….. you get the idea.

 

[Mach1E]

More efficient with windows up and A/C on.
Remember, the A/C compressor is running anyway so might as well get the benefit.

It’s not though.

Compressor doesn’t run with the a/c off.

It spins freely (a/c compressors have a clutch).

 

[SnBGC]

It’s not though.

Compressor doesn’t run with the a/c off.

It spins freely (a/c compressors have a clutch).

No clutch in the Mach-E.
It runs anyway to chill the battery.
Connect a scan tool, it will show the A/C compressor running just while driving around. HvAC can be turned off and the compressor will still function.

 

[ChuckA]

I always drive windows up, a/c on, and recirc on. Too many dead skunks and soot blowing trucks in my neighborhood.

 

[Mach1E]

No clutch in the Mach-E.
It runs anyway to chill the battery.
Connect a scan tool, it will show the A/C compressor running just while driving around. HvAC can be turned off and the compressor will still function.

Well…… that would change everything.

Then why does energy usage list climate when the AC is running?

 

[babgvant]

Yes it’s measurable.

So is the 1/2 hp that an a/c system uses.

So if you’re comparing 1/2 hp from a/c vs 1/2 hp from windows down drag…….. you get the idea.

Do you have a source for those numbers? Or did you make them up?

I think it's highly likely that you're creating way more drag with the windows down than electricity consumption from running the AC. Air gets sucked in, swirls around, flaps the rear belts (seriously Ford, did no one test this?), and then is forced out as new air detaches into the interior. You want attachment, and for that air to hang on as long as possible, when the windows are open you're creating a swirling vacuumy mess around the car, this is the opposite of aerodynamic efficiency.

Given that the car was designed with CdA as a priority, it's really hard to see this any other way.

That said, if you want to open your windows, by all means open the windows. I do it too, some days it's nice to drive around with them down and the rear belt flapping .

 

[SnBGC]

Well…… that would change everything.

Then why does energy usage list climate when the AC is running?

Good question. Not sure. I think the car calculates how much energy is for passenger comfort and lists that under Climate Use and the rest goes to Exterior Temp. The Focus Electric called it Other if I remember correctly.

Technically speaking.....the ACCM can regulate the A/C compressor by RPM so in theory it could JUST cool the HVB but when I looked at the components, I didn't see a valve for the cabin so it appears if the A/C compressor is on, then it cools the evaporator anyway so might as well blow some air across it and cool the cabin.

If it is cool and comfortable enough to roll down the windows then not much energy would be used by the A/C anyway.

In the end, it is a minor difference either way. If hyper-miling, then keep the windows rolled up. ?

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